It is well known that as quantity of plastics manufactured increases in recent years, the disposal of the scrap has become a problem. There are some plastics for which the technology for recycling has been developed to a practical stage for recycling of polyolefin plastics, which are said to represent approximately one half of the quantity of thermoplastic resins manufactured in Japan, has not yet become satisfactory and effective for practical use except on a small scale. Thermal cracking methods, as described for example, in U.S. Pat. No. 3,956,414 (Oshima), are disadvantageous because considerable amounts of waxy materials are formed, and also because carbon is formed and becomes attached to the inner walls of the reaction vessels used for the processing. It has therefore not been practicable to put these methods to practical use for commonly used plastics.
Proposals for processing scrap plastics have been made in the past. For example, U.S. Pat. Nos. 4,108,730 and 4,175,211 (Chen) disclose a process for converting polymeric wastes such as rubber tires, plastic ware and scrap plastic to more valuable liquid, solid and gaseous hydrocarbon products by mixing the waste with a refractory petroleum stream and catalytically cracking the mixture. Suitable petroleum streams include fractions produced by catalytic cracking, for example, heavy cycle oil (HCO). The disadvantage of this method is, however, that it needs to be operated in proximity to a catalytic cracker which therefore precludes it from being used on a relatively smaller scale close to the source of the plastic waste. In addition, relatively large volumes of the petroleum stream are necessary for mixing with the scrap.
U.S. Pat. No. 4,118,281 (Yan) describes a process for converting solid wastes including rubbers, plastics and other material to gas, oil and coke by slurrying the waste with a petroleum stream, especially the heavy recycle fraction from a coker unit and coking the resulting mixture. The products of the coking may be used as a catalytic cracker feed to produce high yields of gasoline. Although this process is compatible with conventional petroleum refining technology it also requires to be carried out at the refinery and requires relatively large volumes of the petroleum stream to dissolve or slurry the waste before it is coked. It would be desirable to eliminate the necessity for using the separate petroleum stream for mixing with the waste so as to permit the process to be carried out effectively close to the soure of the waste with only the high value liquid conversion products being transported off-site.